Question

CREATE TABLE [LB].[Orders]
(
    [OrderID] [bigint] IDENTITY(1,1) NOT NULL,
    [OrderDate] [date] NOT NULL,
    [Status] [nvarchar](max) NULL,

    CONSTRAINT [PK_MasterOrderID] 
        PRIMARY KEY CLUSTERED ([OrderID] ASC)
) 

CREATE NONCLUSTERED INDEX [PK_Index]  
    ON [BTP_NYA].[LB].[Orders] ([OrderDate]); 

CREATE UNIQUE NONCLUSTERED INDEX [IX_OrderID_OrderDate]  
    ON [BTP_NYA].[LB].[Orders] ([OrderDate],[OrderID]);

我正在尝试加快此查询：

SELECT * FROM [BTP_NYA].[XX].[Orders] WHERE [OrderDate] = '20170921' AND [OrderID] = 62192

为什么此查询不使用我的IX_OrderID_OrderDate索引？我怎么能更快？

<?xml version="1.0" encoding="utf-16"?>
<ShowPlanXML xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" Version="1.2" Build="12.0.4232.0" xmlns="http://schemas.microsoft.com/sqlserver/2004/07/showplan">
  <BatchSequence>
    <Batch>
      <Statements>
        <StmtSimple StatementCompId="1" StatementEstRows="1" StatementId="1" StatementOptmLevel="TRIVIAL" CardinalityEstimationModelVersion="120" StatementSubTreeCost="0.0032831" StatementText="SELECT * FROM [BTP_NYA].[LB].[Orders] WHERE [OrderDate]=@1 AND [OrderID]=@2" StatementType="SELECT" QueryHash="0x547011333B745205" QueryPlanHash="0xD16E72141B86DC03" RetrievedFromCache="true">
          <StatementSetOptions ANSI_NULLS="true" ANSI_PADDING="true" ANSI_WARNINGS="true" ARITHABORT="true" CONCAT_NULL_YIELDS_NULL="true" NUMERIC_ROUNDABORT="false" QUOTED_IDENTIFIER="true" />
          <QueryPlan DegreeOfParallelism="0" NonParallelPlanReason="NoParallelPlansInDesktopOrExpressEdition" CachedPlanSize="32" CompileTime="0" CompileCPU="0" CompileMemory="144">
            <MemoryGrantInfo SerialRequiredMemory="0" SerialDesiredMemory="0" />
            <OptimizerHardwareDependentProperties EstimatedAvailableMemoryGrant="836385" EstimatedPagesCached="209096" EstimatedAvailableDegreeOfParallelism="2" />
            <RelOp AvgRowSize="12369" EstimateCPU="0.0001581" EstimateIO="0.003125" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Row" EstimateRows="1" LogicalOp="Clustered Index Seek" NodeId="0" Parallel="false" PhysicalOp="Clustered Index Seek" EstimatedTotalSubtreeCost="0.0032831" TableCardinality="59123">
              <OutputList>
                <ColumnReference Database="[BTP_NYA]" Schema="[LB]" Table="[Orders]" Column="OrderID" />
                <ColumnReference Database="[BTP_NYA]" Schema="[LB]" Table="[Orders]" Column="OrderDate" />
                <ColumnReference Database="[BTP_NYA]" Schema="[LB]" Table="[Orders]" Column="Status" />
              </OutputList>
              <RunTimeInformation>
                <RunTimeCountersPerThread Thread="0" ActualRows="1" ActualEndOfScans="1" ActualExecutions="1" />
              </RunTimeInformation>
              <IndexScan Ordered="true" ScanDirection="FORWARD" ForcedIndex="false" ForceSeek="false" ForceScan="false" NoExpandHint="false" Storage="RowStore">
                <DefinedValues>
                  <DefinedValue>
                    <ColumnReference Database="[BTP_NYA]" Schema="[LB]" Table="[Orders]" Column="OrderID" />
                  </DefinedValue>
                  <DefinedValue>
                    <ColumnReference Database="[BTP_NYA]" Schema="[LB]" Table="[Orders]" Column="OrderDate" />
                  </DefinedValue>
                  <DefinedValue>
                    <ColumnReference Database="[BTP_NYA]" Schema="[LB]" Table="[Orders]" Column="Status" />
                  </DefinedValue>
                </DefinedValues>
                <Object Database="[BTP_NYA]" Schema="[LB]" Table="[Orders]" Index="[PK_MasterOrderID]" IndexKind="Clustered" Storage="RowStore" />
                <SeekPredicates>
                  <SeekPredicateNew>
                    <SeekKeys>
                      <Prefix ScanType="EQ">
                        <RangeColumns>
                          <ColumnReference Database="[BTP_NYA]" Schema="[LB]" Table="[Orders]" Column="OrderID" />
                        </RangeColumns>
                        <RangeExpressions>
                          <ScalarOperator ScalarString="CONVERT_IMPLICIT(bigint,[@2],0)">
                            <Convert DataType="bigint" Style="0" Implicit="true">
                              <ScalarOperator>
                                <Identifier>
                                  <ColumnReference Column="@2" />
                                </Identifier>
                              </ScalarOperator>
                            </Convert>
                          </ScalarOperator>
                        </RangeExpressions>
                      </Prefix>
                    </SeekKeys>
                  </SeekPredicateNew>
                </SeekPredicates>
                <Predicate>
                  <ScalarOperator ScalarString="[BTP_NYA].[LB].[Orders].[OrderDate]=CONVERT_IMPLICIT(date,[@1],0)">
                    <Compare CompareOp="EQ">
                      <ScalarOperator>
                        <Identifier>
                          <ColumnReference Database="[BTP_NYA]" Schema="[LB]" Table="[Orders]" Column="OrderDate" />
                        </Identifier>
                      </ScalarOperator>
                      <ScalarOperator>
                        <Convert DataType="date" Style="0" Implicit="true">
                          <ScalarOperator>
                            <Identifier>
                              <ColumnReference Column="@1" />
                            </Identifier>
                          </ScalarOperator>
                        </Convert>
                      </ScalarOperator>
                    </Compare>
                  </ScalarOperator>
                </Predicate>
              </IndexScan>
            </RelOp>
            <ParameterList>
              <ColumnReference Column="@2" ParameterCompiledValue="(62192)" ParameterRuntimeValue="(62192)" />
              <ColumnReference Column="@1" ParameterCompiledValue="'20170921'" ParameterRuntimeValue="'20170921'" />
            </ParameterList>
          </QueryPlan>
        </StmtSimple>
      </Statements>
    </Batch>
  </BatchSequence>
</ShowPlanXML>

Answer 1

未使用非聚集索引的原因是因为使用唯一主键聚簇索引选择单行更有效。你不能比这更快地选择单行的所有列（禁止内存表中的哈希索引）。

Answer 2

它在PK_MasterOrderID上进行聚簇索引搜索。

这是因为您执行select *而IX_OrderID_OrderDate不包含任何列。

如果要使用

创建索引

CREATE UNIQUE NONCLUSTERED INDEX [IX_OrderID_OrderDate]  
ON [BTP_NYA].[LB].[Orders] ([OrderDate],[OrderID]) INCLUDE([all], [selected], [columns]);

，它会被使用。

为什么查询不使用我的索引？

2 个答案: